After being shut down for more than a week due to a "security incident," Macmillan US's warehouse resumed its core operations on July 4. As part of coming back online, the warehouse is now processing, shipping, and receiving orders.

To guard against further damage from the attack on its systems, Macmillan had taken its systems offline last month—something that prevented it from processing, shipping, and receiving orders. Late last week, it was able to receive orders, but not process them.

In its newest update, Macmillan said it is a adding more resources "to quickly work through the backlog of orders submitted while our systems were down and we do not anticipate the need to move any on-sale dates at this time."

While its systems were down, Macmillan's offices were closed, but with almost all systems restored for employees, Macmillan expects to reopen its offices at 120 Broadway in New York on July 7.